Refrigeration & Air-Conditioning Practice Set-3

May 18, 2021

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1. If a heat pump cycle operates between the condenser temperature of +27°C and evaporator temperature of -23°C, then the Carnot COP will be

1.2

0.2

2. The atmospheric air at dry bulb temperature of 15°C enters a heating coil maintained at 40°C. The air leaves the heating coil at 25°C. The bypass factor of the heating coil is

0.4

0.376

0.6

0.67

3. The domestic refrigerator uses following type of compressor

Axial

Piston type reciprocating

Centrifugal

Miniature sealed unit

4. The value of C.O.P in vapour compression cycle is usually

Any one of the above

Always more than unity

Always less than unity

Equal to unity

5. Which of the following cycles uses air as the refrigerant?

Ericson

Stirling

Carnot

Bell Coleman

6. The curved lines on a psychrometric chart indicates

Dew point temperature

Wet bulb temperature

Dry bulb temperature

Relative humidity

7. The general rule for rating refrigeration systems (excepting for CO₂ system) is to approximate following h.p. per ton of refrigeration

0.5 to 0.8 h.p. per ton of refrigeration

2 to 5 h.p. per ton of refrigeration

1 to 2 h.p. per ton of refrigeration

0.1 to 0.5 h.p. per ton of refrigeration

8. Critical temperature is the temperature above which

Water will evaporate

A gas will never liquefy

A gas will immediately liquefy

Water will never evaporate

9. The freezing point of sulphur dioxide is

-56.6°C

-77.7°C

-75.2°C

-135.8°C

10. Most thermostatic expansion valves are set for a superheat of

10°C

20°C

15°C

5°C

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11. When the temperature of the surrounding is higher than the temperature of the body, then the heat loss by convection from the body to the surrounding will be

Positive

Negative

None of these

Zero

12. Mass flow ratio of NH₃ in comparison to Freon-12 for same refrigeration load and same temperature limits is of the order of

1: 1

9: 1

1: 3

1: 9

13. The refrigerant after condensation process is cooled below the saturation temperature before throttling. Such a process is called

Sub-cooling or under-cooling

Normal cooling

None of these

Super-cooling

14. For obtaining high COP, the pressure range of compressor should be

Optimum

High

Any value

Low

15. On the pressure-enthalpy diagram, condensation and desuperheating is represented by a horizontal line because the process

Takes place at constant entropy

Involves no change in volume

Takes place at constant temperature

Takes place at constant pressure

16. A thermostatic expansion valve in a refrigeration system

Is suitable only for constant load systems

Ensures the evaporator completely filled with refrigerant of the load

Maintains different temperatures in evaporator in proportion to load

None of the above

17. The boiling point of ammonia is

-10.5°C

-30°C

-33.3°C

-77.7°C

18. A human body feels comfortable when the heat produced by the metabolism of human body is equal to the

(A) Heat dissipated to the surroundings

(B) Heat stored in the human body

(D) Difference of (A) and (B)

19. In a refrigeration system, heat absorbed in comparison to heat rejected is

Same

More for small capacity and less for high capacity

Less

20. In a flooded evaporator refrigerator, an accumulator at suction of compressor is used to

Collect liquid refrigerant and prevent it from going to compressor

Detect liquid in vapour

Superheat the vapour

Collect vapours

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21. The vapour compression refrigerator employs the following cycle

Reversed Carnot

Reversed Rankine

Carnot

Rankine

22. In a lithium bromide absorption refrigeration system

Lithium bromide is used as a refrigerant and water as an absorbent

Water is used as a refrigerant and lithium bromide as an absorbent

None of these

Ammonia is used as a refrigerant and lithium bromide as an absorbent

23. Freon group of refrigerants are

Non-inflammable and toxic

Toxic

Inflammable

Nontoxic and non-inflammable

24. A certain refrigerating system has a normal operating suction pressure of 10 kg/cm gauge and condensing pressure of about 67 kg/cm. The refrigerant used is

Ammonia

Carbon dioxide

Brine

Freon

25. A bootstrap air cooling system has

Two heat exchangers

Three heat exchangers

One heat exchanger

Four heat exchangers

26. The condition of refrigerant after passing through the condenser in a vapour compression system is

Dry saturated vapour

Superheated vapour

Wet vapour

Saturated liquid

27. The capillary tube, as an expansion device, is used in

All of these

Room air conditioners

Water coolers

Domestic refrigerators

28. A reversible engine has ideal thermal efficiency of 30%. When it is used as a refrigerating machine with all other conditions unchanged, the coefficient of performance will be

4.33

3.33

1.33

2.33

29. Cooling water is required for following equipment in ammonia absorption plant

Evaporator

Condenser, absorber and separator (rectifier)

Condenser

Absorber

30. Highest temperature encountered in refrigeration cycle should be

At critical Temperature

Near critical temperature of refrigerant

Much below critical temperature

Above critical temperature

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31. In actual air-conditioning applications for R-12 and R-22, and operating at a condenser temperature of 40° C and an evaporator temperature of 5° C, the heat rejection factor is about

1.25

5.12

2.15

32. Rating of a domestic refrigerator is of the order of

40 tons

0.1 ton

5 tons

10 tons

33. Which of the following is not a desirable property of a refrigerant?

Good electrical conductor

Large latent heat

Low boiling point

High risibility with oil

34. Which of the following statement is correct?

(A) The human body can lose heat even if its temperature is less than the atmospheric temperature.

(D) Both (A) and (B)

(B) The increase in air movement increases the evaporation from the human body.

35. In a refrigeration system, the expansion device is connected between the

Evaporator and compressor

Compressor and condenser

Condenser and receiver

Receiver and evaporator

36. The change in evaporator temperature in a refrigeration cycle, as compared to change in condenser temperature, influences the value of C.O.P.

Less

Unpredictable

Equally

37. The bank of tubes at the back of domestic refrigerator is

Capillary tubes

Evaporator tubes

Condenser tubes

Refrigerant cooling tubes

38. The operating pressure for refrigerating units using R-12 as a refrigerant is

15 bar

30 bar

2 bar

8 bar

39. The minimum temperature to which water can be cooled in a cooling tower is

Dew point temperature of air

Wet bulb temperature of air

Dry bulb temperature of air

Ambient air temperature

40. The C.O.P. of a refrigerator working on a reversed Carnot cycle is (where T₁ = Lowest absolute temperature, and T₂ = Highest absolute temperature)

(T₁ - T₂)/T₁

(T₂ - T₁)/T₁

T₂/ (T₂ - T₁)

T₁ / (T₂ - T₁)

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A Demrot is the founder of VideRime Online Learning, a leading engineering website. He did his BE Civil and M.Tech Structure from RGPV University, Bhopal and has been working as an Assistant Professor in a reputed college.

Refrigeration & Air-Conditioning Practice Set-3

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